A thrombus is a blood clot that forms in a blood vessel and remains there. This can result in damage, destruction (infarction), or even death of the tissue (necrosis) in that area. Thrombus surgery is a common procedure. There have been many different surgical tools developed for thrombus removal. These include tools that remove the thrombus by mechanical force, use of thrombolytic agents, and ultrasonic energy. However, these techniques suffer from a number of drawbacks including, but not limited to, low efficiency and damage to blood vessel wall.
Piezoelectric devices for thrombolytic ablation have been developed. The actuator has an external power generator that supplies the actuator with the electrical energy required to produce ultrasonic energy. A transducer of lead zirconate titanate (“PZT”) crystals converts the electrical energy to high-power ultrasonic waves. An ultrasound catheter, connected at the proximal end of the transducer, transmits the ultrasonic waves to the target thrombus at its distal end. The ablation of the thrombus by ultrasound is by cavitation in the blood clot caused by the ultrasonic waves.
Ultrasonic tissue ablation exhibits tissue selectivity. The susceptibility of biological tissues to ultrasonic disruption is inversely proportional to their elastic recoil, which represented by their collagen and elastin content. While thrombi are poorly endowed with elastic elements, they are highly susceptible to ultrasonic ablation. Conversely, the normal arterial wall, which is rich with compliant matrix of collagen and elastin, is relatively spared. Since cavitation is bioselective, aortic walls are resistant to cavitation leaving only the thrombus ablated by the actuator described above.
One example of an ultrasonic catheter used to treat human blood vessels delivers solutions containing dissolution compounds directly to the occlusion site to remove or reduce the occlusion. In addition, ultrasonic energy is generated by an ultrasound assembly and is used to enhance the therapeutic effect of the dissolution compounds. Since only the catheter is inserted into the blood vessel and the transducer is outside the body, the input power needed will be high to provide sufficient ultrasound energy to the catheter for thrombolysis. Also, due to the long length of the catheter energy loss along the catheter will be high. This means that efficiency will decrease due to the energy loss.
Another example uses a transcranial ultrasound thrombolysis system that uses ultrasonic energy in combination with thrombolytic agents to assist in dissolving intracranial thrombi and to enhance the efficacy of the thrombolytic agents. However, the large dimensions of the system have limited its practical application.
A further example of an ultrasonic medical device is used to treat deep vein thrombosis by using ultrasonic energy with plurality of transverse node and anti-nodes along the longitudinal axis of the ultrasonic probe to generate cavitation to ablate the thrombus and treat deep vein thrombosis. The transverse ultrasonic vibration may damage surrounding cells instead of just the thrombus. Also, it is less localized to the thrombus as only a catheter is inserted into the body.
The prior art does not provide a suitable device to be inserted into body that is able to ablate, emulsify and remove the thrombus. The prior art does not provide a solution to better localize to the thrombus site to have higher precision as is required in human applications. The prior art uses high input power to generate low frequency ultrasound energy. They suffer from large energy losses during the conversion. Thus, there remains a need for a device that is small in size so that can be inserted into body and is able to ablate, emulsify and remove thrombus. This is preferably in a more localized manner.